Ethers are an important raw material, solvent, and intermediate used in organic synthesis, as oxygenators for fuels, as diesel fuel additives, in pharmaceuticals, in agrochemicals, in refrigeration applications, as flavoring agents, and in many other applications.
A number of scientific publications and patents have studied, or proposed, the use of alkyl tetrahydrofurfuryl ethers, for example, for a diverse array of applications. In 1930, Kirner synthesized a small library of alkyl tetrahydrofurfuryl ethers, and analyzed their use as an anesthetic and their toxicity in mice and guinea pigs. W. R. Kirner, Alpha-Tetrahydrofurfuryl Chloride and Alpha-Tetrahydrofurfuryl Ethers, Journal of the American Chemical Society, 1930, 52, 3251. Some published works show the utility of these compounds as structural modifiers in rubbers. Modification of rubber with various alkyl tetrahydrofurfuryl ethers increases the static friction coefficient of the product. Additionally, these compounds have been proposed as components of heat pumps, paint strippers, and as fuel additives.
There is a large market for these compounds, and there are proposed methods for their synthesis. For example, current syntheses of ethyl tetrahydrofurfuryl ether (ETFE) are described in U.S. Pat. No. 4,305,878 to Chu, et al. The method disclosed in the Chu et al. patent describes the purification of ETFE via multiple extractions using multiple calcium chloride and other aqueous salts, followed by fractional distillation. Chu specifically states the difficulty in separating ETFE from tetrahydrofurfuryl alcohol (THFA) and alcohol using distillation and that multiple aqueous extractions were required to remove THFA to below acceptable levels. This requirement for multiple extractions and distillations is both inefficient and undesirable.
Cao, et al., “Solid acid-catalyzed conversion of furfuryl alcohol to alkyl tetrahydrofurfuryl ether”, 2015, Catalysis Communications, Volume 58, Pages 76-79) disclose a cumbersome process which uses at least two (2) separate catalytic steps with low yields (ETFE—40.6% [at 55° C.]) and low purity.
One tetrahydrofurfuryl ether that has been cited as difficult to obtain is bis(tetrahydrofurfuryl) ether (BTHFE). The one previous report of its synthesis lacked an in-depth characterization of the compound, leaving some doubt as to the true identity of the reported product. L. M. Prutkov, I. K. Sanin, I. V. Kamenskii, Bis(tetrahydrofurfuryl) ether, Khim. Geterotsikl. Soedin, 632 (1966).
The current invention provides novel synthesis and purification techniques in which no extractions are necessary, and in which at least 90% purity, and greater than 98% purity ether has been obtained in one or two steps using fractional distillation in the presence of an excess of a reactive element. This method is particularly useful for the synthesis and purification of tetrahydrofurfuryl ethers, such as alkyl tetrahydrofurfuryl and bis(tetrahydrofurfuryl) ethers.
It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not to be viewed as being restrictive of the invention, as claimed. Further advantages of this invention will be apparent after a review of the following detailed description of the disclosed embodiments.